1. Field of the Invention
The present invention relates to an aluminum alloy brazing sheet used for a heat exchanger of an automobile and the like.
2. Description of the Related Art
As a raw material for a heat exchanger of an automobile and the like, a variety of aluminum alloy brazing sheets (may be hereinafter simply referred to as “brazing sheet”) disposed with a brazing filler material and a sacrificial anode material on one face or both faces of a core material are generally used. In the past, as the core material for the brazing sheet, Al—Mn-based aluminum alloy 3003 was used, however the brazing sheet using the core material had not sufficient post-braze strength and corrosion resistance.
Therefore, technologies for improving the post-braze strength and corrosion resistance of the brazing sheet have been proposed. For example, there is a technology improving the post-braze strength without deteriorating the brazability of a brazing sheet by adding a predetermined amount of Mg to a sacrificial anode material of the brazing sheet (for example, Japanese Patent No. 2564190; see the column in the right in p. 2). More specifically, according to the technology, Mg added to the sacrificial anode material and Si present in the brazing filler material migrate into the core material in heating for brazing and Mg2Si is generated inside the core material, thereby the post-braze strength of the brazing sheet is improved and deterioration of the brazability is avoided because Mg added to the sacrificial anode material does not reach the brazing filler material.
Also, there is a technology improving the post-braze strength and corrosion resistance of a brazing sheet by adding a predetermined amount of Cu to a core material of the brazing sheet and making the sacrificial anode material of a predetermined thickness while adding a predetermined amount of Zn to a sacrificial anode material (for example, Japanese Patent No. 3276790; see the paragraph 0013). More specifically, according to the technology, the corrosion resistance is improved by Zn added to the sacrificial anode material and making the sacrificial anode material of a predetermined thickness, and the post-braze strength is improved by strengthening of solid solution by Cu added to the core material.
However, the requirement on the heat exchanger of an automobile and the like in recent years extends not only to improvement of the post-braze strength and corrosion resistance as described above but also to size reduction and weight reduction. In order to meet the requirements of the size reduction and weight reduction, the thickness of the material of the heat exchanger should be reduced, however the strength and corrosion resistance are deteriorated as the thickness of the material of the heat exchanger is reduced. In addition, thinner gauge down of the material of the heat exchanger becomes a cause of generating welding defect in high frequency welding.